1. Field of the Invention
The present invention relates to a telescopic steering column device, and, more particularly, to a telescopic steering column device arranged in such a manner that the overall length of the steering column through which steering shaft passes can be expanded/contracted so as to adjust the position of a steering wheel disposed at the end portion of the steering shaft for the purpose of being fitted to the body of a driver or the attitude of a driver.
2. Related Background Art
Hitherto, there has been a known telescopic steering column device arranged in such a manner that the position of the steering wheel can be adjusted so as to be fitted to the body of a driver or the attitude of a driver.
FIGS. 1 to 3 illustrate an example of a telescopic steering column of the type described above.
Referring to FIGS. 1 to 3, reference numeral 1 represents an adjust lever of the telescopic steering column device with which the locked state can be cancelled when it is operated at the time of performing an adjustment operation. With the thus realized cancelled state maintained, the overall length of a steering column 4, constituted by telescopically combining an outer column 2 with an inner column 3, is expanded/contracted. As a result, an end portion of a steering shaft 5 which is also telescopically constituted is displaced in a direction designated by an arrow a shown in FIGS. 1 and 2 so that the longitudinal position of a steering wheel (omitted from illustration) secured to the end portion of the steering shaft 5 is adjusted.
That is, the steering column 4 forming the telescopic steering column device is constituted by the outer column 2 and the inner column 3 each of which is in the form of a cylinder and which are telescopically combined with each other.
A drive-side steering shaft 5a, to which the steering wheel is fastened, is borne on the inner side of the inner column 3 via a pair of rolling bearings 7 and 8. The steering shaft 5a has a spline fastening portion 9 formed so as to be engaged with a driven-side steering shaft 5b. As a result, the drive-side steering shaft 5a is expanded/contracted with respect to the position of the driven-side steering shaft 5b in accordance with the expansion/contraction of the steering column 4.
A lock bracket 10, formed by bending a metal plate into a U-shape facing sidewards, is secured to the intermediate portion of the outer column 2. That is, the two side portions of a supporting plate portion 11 disposed in the central portion of the lock bracket 10 are bent perpendicularly in the same direction so that fastening plate portions 12 are formed. When the lock bracket 10 thus arranged is secured to the outer column 2, the outer column 2 is inserted into circular holes 13 formed in each of the fastening portions 12. Furthermore, the portions around the circular holes 13 and the outer surface of the outer column 2 are welded to one another.
A nut member 14 is secured to the central portion of the supporting plate portion 11 projecting to the side portion (downwards when viewed in FIG. 2 and to the left when viewed in FIG. 3) of the outer column 2, the lock bracket 10 being secured to the intermediate portion of the outer column 2.
A rectangular opening 15 is formed in the side surface of the outer column 2 at a position corresponding the nut member 14. A lock member 16 is positioned within the opening 15 in such a manner that the lock member 16 can be moved inwards and outwards (in the vertical direction when viewed in FIG. 2 and in the lateral direction when viewed in FIG. 3). An inner surface 16a of the lock member 16 thus positioned within the opening 15 is arranged to be in the form of a recess of a circular arc, the inner surface 16a being brought into contact with the outer surface of the inner column 3.
A lock screw 18 is fitted in a thread hole 17 formed in the nut member 14 secured to the central portion of the supporting plate portion 11. The inner end surface of the lock screw 18 (the lower end surface when viewed in FIG. 2 and the left end surface when viewed in FIG. 3) is positioned in contact with the outer surface of the lock member 16. Furthermore, the base portion of the adjust lever 1 is secured to the outer end surface of the lock screw 18. As a result, when the adjust lever 1 is operated and the lock screw 18 is thereby rotated, the inner surface 16a of the lock member 16 can be abutted against the outer surface of the inner column 3 and can be separated from the same.
A projection portion 20 is formed on the inner surface of the lock member 16, while an elongated hole 21 elongating in the axis direction (in the lateral direction when view in FIG. 2 and the perpendicular direction to the drawing sheet of FIG. 3) is formed in the side surface of the inner column 3 at the position corresponding the projection portion 20. The thus formed projection portion 20 is positioned loosely in the elongated hole 21 so that the axial displacement of the inner column 3 with respect to the position of the outer column 2 is allowed and its rotation in the torsional direction is prevented.
The overall length of the steering column 4 of the telescopic steering column device thus constituted is adjusted as follows:
First, the adjust lever 1 is operated so as to rearwards (to the left when viewed in FIG. 3) move the lock screw 18, causing the force with which the lock member 16 is abutted against the outer surface of the inner column 3 to be released. As a result, a state in which the inner column 3 can be freely moved inside the outer column 2 is realized.
With the above-described state maintained, a steering wheel (omitted from illustration) secured to an end portion of the drive-side steering shaft 5a is pushed or drawn so that the longitudinal position of the steering wheel is adjusted. In accordance with the pushing or drawing of the steering wheel, the relative position from the driven-side steering shaft 5b is displaced by the spline fastening portion 9 disposed in the intermediate portion of the drive-side steering shaft 5a. Furthermore, the inner column 3, disposed on the outer surface of the drive-side steering shaft 5a via the pair of rolling bearings 7 and 8, is longitudinally displaced.
If the longitudinal positional adjustment of the steering wheel has been completed as a result of the above-described operation, the adjust lever 1 is operated so that the lock screw 18 is moved forwards (to the right when viewed in FIG. 3). The thus moved lock screw 18 abuts the lock member 16 against the outer surface of the inner column 3. As a result, large frictional force acts between the inner surface 16a of the lock member 16 and the outer surface of the inner column 3, causing the inner column 3 to be supported on the inside of the outer column 2 in such a manner that the inner column 2 cannot be displaced. Therefore, the state in which the steering wheel is supported at a position after the adjustment is maintained.
However, the conventional telescopic steering column device structured and operated as described above arises the following problems to be overcome:
The inner column 3 which can be displaced within the outer column 2 is arranged to be able to be displaced in the axial direction (in the lateral direction when viewed in FIG. 2) but it must be arranged so as not to rotate in the torsional direction.
Therefore, in the case of the conventional telescopic steering column device shown in FIGS. 2 and 3, a projection portion 20 is formed on the inner surface of the lock member 16, while an elongated hole 21 elongating in the axis direction (in the lateral direction when view in FIG. 2 and the perpendicular direction to the drawing sheet of FIG. 3) is formed in the side surface of the inner column 3 at the position corresponding the projection portion 20. The thus formed projection portion 20 is positioned loosely in the elongated hole 21 so that the axial displacement of the inner column 3 with respect to the position of the outer column 2 is allowed and its rotation in the torsional direction is prevented.
However, it is a complicated work to form the projection portion 20 on the inner surface 16a of the lock member 16 since the inner surface 16a is in the form of a recess of a circular arc. Therefore, the cost for manufacturing the lock member 16 is raised, causing the overall cost for manufacturing the telescopic steering column device to be raised excessively.
Furthermore, as shown in FIG. 4, the conventional structure has been arranged in such a manner that a fastening pin 22 is secured to a portion of the outer column 2 at a position which does not correspond to the above-described opening 15. In addition, the front portion of the thus secured fastening pin 22 and the elongated hole 21 formed in the inner column 3 are loosely engaged with each other so that the axial displacement of the inner column 3 with respect to the position of the outer column 2 is allowed and the rotation of it in the torsional direction is prevented.
However, the second structure shown in FIG. 4 arises a problem in that the cost for manufacturing the telescopic steering column device of this type cannot be satisfactorily reduced since the number of the necessary parts is increased and the part administration and the assembling work become too complicated.
Furthermore, in the conventional telescopic steering column device, the inner diameter of the outer column 2 and the outer diameter of the inner column 3 have been made substantially the same so that the looseness of the inner column 3 in the fixed outer column 2 has been prevented. However, if force for pushing a portion of the inner column 3 is applied due to bending or the like of the steering shaft 5, the frictional force acting between the outer surface of the inner column 3 and the inner surface of the outer column 2 is thereby enlarged. As a result, the steering column 4 is expanded/contracted, causing a problem to be arisen in that the force necessary to displace the inner column becomes too large.
In order to improve the rigidity of the steering column 4 against the force acting in the bending direction, it is effective to elongate length L (see FIG. 12) in which the outer column 2 and the inner column 3 are fastened to each other, the outer column 2 and the inner column 3 constituting the steering column 4.
Furthermore, the distance between the pair of the rolling bearings 7 and 8 cannot be enlarged excessively, the pair of the rolling bearings 7 and 8 being acting to rotatably bearing the steering shaft 5a on the inside of the inner column 3. For example, the rolling bearing 7 on the steering wheel side (on the right side when viewed in FIG. 12) cannot be excessively shifted to right because a variety of switches such as a direction indicator are positioned there.
On the other hand, the excessive shift of the roller bearing 8 positioned opposite to the steering wheel (on the left side when viewed in FIG. 12) encounters a limitation because it is necessary for the amount of the expansion/contraction of the steering column 4 to be secured. That is, as shown in FIGS. 5 and 12, the telescopic steering column device is usually used in combination with a so-called neck-swinging tilt steering which moves relative to a lateral shaft 25 positioned in a relatively upper portion of the steering column device. The neck-swinging tilt steering of the type described above must have a universal joint 26 (see FIG. 12) on an extension line from the above-described lateral shaft 25 so as to establish a connection between the lower end portion of the driven-side steering shaft 5b and the top portion of the lower steering shaft 27. The outer diameter of the portion in which the universal joint 26 is positioned necessarily has a certain degree. Therefore, if a cylindrical portion 6 of the driven-side steering shaft 5a, which supports the inner surface of the roller bearing 8, is extended to the left when viewed in the drawing for the purpose of shifting the roller bearing 8 to the left, distance 1 between the end surface of the cylindrical portion 6 and the portion in which the above-described universal joint 26 is positioned is shortened. As a result, the amount of expansion/contraction of the steering column 4 must be undesirably reduced.
In order to elongate the fastening length L between the outer column 2 and the inner column 3 without shifting the positions of the rolling bearings 7 and 8, it might be considered feasible to employ a structure in which the end portion of the inner column 3 inserted into the outer column 2 is arranged to project over the roller bearing 8. However, the above-described structure in which the end portion of the inner column 3 is simply arranged to project over the roller bearing 8 arises a problem in that the frictional force acting between the outer surface of the inner column 3 and the inner surface of the outer column 2 becomes too large.
That is, in the case where the end portion of the inner column 3 is, as shown in FIG. 6, simply projected over the roller bearing 8, the end portion of the inner column 3 is outwardly expanded as designated by an arrow b shown in FIG. 6, when the roller bearing 8 is press-fitted into the inner portion of the inner column 3. The outer surface of the thus expanded end portion of the inner column 3 is strongly abutted against the inner surface of the outer column 2, causing the frictional force to act on the inner surface. Therefore, the force necessary to expand/contract the steering column 4 becomes too large.
In order to prevent the above-described problem in that the end portion of the inner column 3 is expanded when the roller bearing 8 is press-fitted, it might be considered feasible to employ a structure in which the outer surface of the end portion of the inner column is, as shown in FIG. 7, recessed so as to reduce the thickness. In this case, another problem arises in that the rigidity of the steering column 4 against bending force becomes unsatisfactory since the fastening length between the outer column 2 and the inner column 3 becomes too short.